ISBN 9783843950800

978-3-8439-5080-0, Reihe Verfahrenstechnik

Felix Johannes Preiss
Investigation of droplet deformation and breakup in coaxial orifices during high-pressure homogenization

220 Seiten, Dissertation Karlsruher Institut für Technologie (2022), Softcover, A5

Zusammenfassung / Abstract

The high-pressure homogenization process is a widely used process for the production of emulsions with a small to medium viscosity and a target droplet size of less than 1 µm. Although the process was developed at the end of the 19th century and research on the droplet breakup under different flow conditions has been conducted since the beginning of the 20th century, droplet breakup during the high-pressure homogenization process is not yet fully understood. The objective of this work was to investigate the influence of the stress history on the droplet deformation, the droplet breakup, and the resulting droplet size distribution. To overcome the limited spatial resolution and to reduce the velocity as well as the pressure during the process, a scale-up approach for a high-pressure homogenizer orifice is presented. Droplets are exposed to fast changing stresses during high-pressure homogenization, which results in a complex stress load history that is dependent on the droplet trajectory. These differences in the stress load history lead to stronger deformed droplets with a decreasing distance to the flow channel wall. The stronger deformation and the altered droplet-vortex-interaction of droplets on a trajectory close to the wall lead to smaller droplets after the high-pressure homogenization process compared to droplets on a trajectory on the centerline, whereby a narrower droplet size distribution is also achieved. However, this effect was only found for emulsions with a viscosity ratio greater than 3. In conclusion, a more pronounced droplet deformation can increase the energy efficiency of the high-pressure homogenization process. Furthermore, the droplet deformation prior to the breakup can be used to manipulate the width of the emerging droplet size distribution.